github-oauth-nango-integration

What this skill does

# GitHub OAuth + Nango Integration

## Overview

Implements dual-connection OAuth pattern: one for user identity (`github` integration), another for repository access (`github-app-oauth` integration). This separation enables secure login while maintaining granular repo permissions through GitHub App installations.

## When to Use

- Setting up GitHub OAuth login via Nango
- Implementing GitHub App installation webhooks
- Reconciling OAuth users with GitHub App installations
- Building apps that need both user auth and repo access
- Handling Nango sync webhooks for GitHub data

## Why Two Connections?

GitHub has **two different authentication mechanisms** that serve different purposes:

### GitHub OAuth App (`github` integration)
- **What it is**: Traditional OAuth for user identity
- **What it gives you**: User profile (name, email, avatar, GitHub ID)
- **What it DOESN'T give you**: Access to repositories
- **Use for**: Login, "Sign in with GitHub"

### GitHub App (`github-app-oauth` integration)
- **What it is**: Installable app with granular repo permissions
- **What it gives you**: Access to specific repos the user installed it on
- **What it DOESN'T give you**: User identity (it knows the installation, not who's using it)
- **Use for**: Reading PRs, commits, files; posting comments; webhooks

### The Reconciliation Problem

```
OAuth App alone:  "User [email protected] logged in" → but which repos can they access?
GitHub App alone: "Installation #12345 has access to repo X" → but who is the user?
```

**Solution**: Two separate OAuth flows linked by user ID:

1. **Login flow** → User authenticates → Store user identity + `nangoConnectionId`
2. **Repo flow** → Same user authorizes app → Store repos + link via `ownerId`

This lets you answer: "User [email protected] can access repos X, Y, Z"

## Quick Reference

| Connection Type | Nango Integration | Purpose | Stored In |
|----------------|-------------------|---------|-----------|
| User Login | `github` | Authentication, identity | `users.nangoConnectionId` |
| Repo Access | `github-app-oauth` | PR operations, file access | `repos.nangoConnectionId` |

| Flow | Endpoint | Webhook Type |
|------|----------|--------------|
| Login | `GET /auth/nango-session` | `auth` + `github` |
| Repo Connect | `GET /auth/github-app-session` | `auth` + `github-app-oauth` |
| Data Sync | N/A (scheduled) | `sync` |

## Implementation

### 1. Database Schema

```typescript
// users table - stores login connection
export const users = pgTable('users', {
  id: uuid('id').primaryKey().defaultRandom(),
  githubId: text('github_id').unique().notNull(),
  githubUsername: text('github_username').notNull(),
  email: text('email'),
  avatarUrl: text('avatar_url'),
  nangoConnectionId: text('nango_connection_id'),      // Permanent login connection
  incomingConnectionId: text('incoming_connection_id'), // Temp polling connection
  pendingInstallationRequest: timestamp('pending_installation_request'), // Org approval wait
});

// repos table - stores per-repo app connection
export const repos = pgTable('repos', {
  id: uuid('id').primaryKey().defaultRandom(),
  githubRepoId: text('github_repo_id').unique().notNull(),
  fullName: text('full_name').notNull(),
  installationId: uuid('installation_id').references(() => githubInstallations.id),
  ownerId: uuid('owner_id').references(() => users.id),
  nangoConnectionId: text('nango_connection_id'),  // App connection for this repo
});

// github_installations - tracks app installations
export const githubInstallations = pgTable('github_installations', {
  id: uuid('id').primaryKey().defaultRandom(),
  installationId: text('installation_id').unique().notNull(),
  accountType: text('account_type'),   // 'user' | 'organization'
  accountLogin: text('account_login'),
  installedById: uuid('installed_by_id').references(() => users.id),
});
```

### 2. Constants

```typescript
// constants.ts
export const NANGO_INTEGRATION = {
  GITHUB_USER: 'github',              // Login only
  GITHUB_APP_OAUTH: 'github-app-oauth' // Repo access
} as const;
```

### 3. Login Flow Routes

```typescript
// GET /auth/nango-session - Create login OAuth session
app.get('/auth/nango-session', async (c) => {
  const tempUserId = randomUUID();

  const { sessionToken } = await nangoClient.createConnectSession({
    end_user: { id: tempUserId },
    allowed_integrations: [NANGO_INTEGRATION.GITHUB_USER],
  });

  return c.json({ sessionToken, tempUserId });
});

// GET /auth/nango/status/:connectionId - Poll login completion
app.get('/auth/nango/status/:connectionId', async (c) => {
  const { connectionId } = c.req.param();

  // Check if user exists with this incoming connection
  const user = await userRepo.findByIncomingConnectionId(connectionId);
  if (!user) {
    return c.json({ ready: false });
  }

  // Issue JWT and return
  const token = authService.issueToken(user);
  await userRepo.clearIncomingConnectionId(user.id);

  return c.json({ ready: true, token, user });
});
```

### 4. App OAuth Flow Routes

```typescript
// GET /auth/github-app-session - Create app OAuth session (authenticated)
app.get('/auth/github-app-session', authMiddleware, async (c) => {
  const user = c.get('user');

  const { sessionToken } = await nangoClient.createConnectSession({
    end_user: { id: user.id, email: user.email },
    allowed_integrations: [NANGO_INTEGRATION.GITHUB_APP_OAUTH],
  });

  return c.json({ sessionToken });
});

// GET /auth/github-app/status/:connectionId - Poll repo sync
app.get('/auth/github-app/status/:connectionId', authMiddleware, async (c) => {
  const user = c.get('user');

  // Check for pending org approval
  if (user.pendingInstallationRequest) {
    return c.json({ ready: false, pendingApproval: true });
  }

  // Check if repos synced
  const repos = await repoRepo.findByOwnerId(user.id);
  return c.json({ ready: repos.length > 0, repos });
});
```

### 5. Auth Webhook Handler

```typescript
// auth-webhook-service.ts
export async function handleAuthWebhook(payload: NangoAuthWebhook): Promise<boolean> {
  const { connectionId, providerConfigKey, endUser } = payload;

  if (providerConfigKey === NANGO_INTEGRATION.GITHUB_USER) {
    return handleLoginWebhook(connectionId, endUser);
  }

  if (providerConfigKey === NANGO_INTEGRATION.GITHUB_APP_OAUTH) {
    return handleAppOAuthWebhook(connectionId, endUser);
  }

  return false;
}

async function handleLoginWebhook(connectionId: string, endUser?: EndUser) {
  // Fetch GitHub user info via Nango
  const githubUser = await nangoService.getGitHubUser(connectionId);

  // Check if user exists
  const existingUser = await userRepo.findByGitHubId(String(githubUser.id));

  if (existingUser) {
    // Returning user - store temp connection for polling
    await userRepo.update(existingUser.id, {
      incomingConnectionId: connectionId,
    });
    // Delete duplicate connection later
    await nangoService.deleteConnection(connectionId);
  } else {
    // New user - create record
    const user = await userRepo.create({
      githubId: String(githubUser.id),
      githubUsername: githubUser.login,
      email: githubUser.email,
      avatarUrl: githubUser.avatar_url,
      nangoConnectionId: connectionId,
      incomingConnectionId: connectionId,
    });

    // Update connection with real user ID
    await nangoService.patchConnection(connectionId, {
      end_user: { id: user.id, email: user.email },
    });
  }

  return true;
}

async function handleAppOAuthWebhook(connectionId: string, endUser?: EndUser) {
  const userId = endUser?.id;
  if (!userId) throw new Error('No user ID in app OAuth webhook');

  const user = await userRepo.findById(userId);
  if (!user) throw new Error('User not found');

  try {
    // Fetch repos user has access to
    const repos = await githubService.getInstallationReposRaw(connectionId);

    // Sync repos to database
    for (const repo of repos) {
      await repoRepo.upsert({
        githubRepoId: String(re